Manufacture of ceramics



Jan. 3, 1961 J. L.. PARK, JR 2,966,719

MANUFACTURE oF CERAMICS Filed June 15, 1954 L l l MMX ,4%

Unite 2,966,719 MANUFACTURE OF CERAMICS Filed June 15, 1954, Ser. No.436,850

15 Claims. (Cl. 25-156) This invention relates to a solvent, moldable,flexible, vitriable ceramic-particulate films and masses which remainundeteriorated during storage before further processing; to a process ofmaking the same; and more particularly, to the manufacture of thinceramic dielectrics therefrom.

In the manufacture of ceramics, the .evaporation of volatileconstituents from a slip of inorganic materials has been accomplished toprovide, before firing, a bonedry replica of the article to be vitried,i.e., Vformed into a ceramic. This drying to rigidity has beenconsidered a required step inasmuch as it has been thought that thegreatest shrinkage of a piece should take place under conditions whereit could be observed, i.e., before firing.

In recent years interest has been stimulated in making extremely thinceramic articles for use in a dielectric function, particularly asinsulators, components of capacitors and the like. The manufacture ofthese thin ceramic sections, however, presents difliculties inasmuch asa thin, bone-dry specimen, being stiff and brittle, which has beenconsidered the nature of all ceramics before firing, is easily brokenand cannot be cut or trimmed without accumulating a number of defectiveforms which must be rejected with a consequent waste of material.Furthermore, known methods of manufacturing thin ceramics have not beenreliable in giving uniformly thin, nor extremely thin, products.

This invention provides dry, flexible, cohesive, ceramicparticulatefilms which may be cut easily to any desired dimensions, and which maylbe coiled or otherwise changed in shape immediately prior to tiring,without giving rise to an untoward incidence of faulty specimens and thewaste occasioned thereby. These films remain in a state which may betermed leather-hard even when dry, that is, even after the volatiletemporary vehicle has been removed before firing. They may vbe formed asthin as on the order of l mil in thickness, may be manipulated much thesame as tapes, and may be fabricated convenientlyto any desired length.

Another advantage of this invention is that these films of dried,flexible, dense, vitriable, ceramic-particulate materials may be storedindefinitely before further processing and still retain their exibility,their moldability and freedom from undesirable cracks, pinholes andparticulate disruption. Consequently, these films may be manufactured inexcess of any immediate requirements and stored or otherwise handleduntil needed. They are tough, may be processed in an automatic mannerthrough working machinery such as cutters, stampers, molders, rollers,and thereafter may be tired to vitrication by conventional methods.

The thin films of this invention may be made by a process of extremesimplicity requiring but a few active steps and but few precautions ascompared to prior processes of making thin sheets of ceramic-particulateto be fired to a ceramic condition. Yet, by the process herein setforth, thin dielectric ceramics can more easily be made thinner thanpreviously realized.

States Pate f 2,966,719 `'Patented Jan. 3, .1.961

ice

One form of `apparatus suitable for carrying out the process of myinvention is illustrated schematically in the attached drawings forminga part of this specification.

Fig. `l is a side-view, schematic illustration of apparatus which maybeused in carrying out the method of coating and drying a slip ofceramic-particulate. Fig. 2 is a schematic illustration of the method ofcutting the tape supported lilms hereof. Fig. 3 is a cross-section ofcutting surfaces .taken 'along lines 3 3 of Fig. 2. Fig. 4 is a top-viewof a cut lilm of ceramic-particulate material supported by the tape.Fig. 5 is a side-view of the peeling operation to remove theceramicparticulate yfilm from the tape.

ln carrying out the process of kthis invention, a slip .of finelydivided ceramic powder is first compounded by mixing together ,thepowder, an organic volatile solvent, a wetting agent, and an organicbinder composition to be hereinafter described. Conventional methods ofcompounding this slip may be employed but it must be thoroughly mixed toa homogeneous suspension in order to avoid undesirable striations,fractures or areas of poor strength in the fired end product. The slipis `deposited on a flexible moving tape support, spread, leveled, andslightly compressed into a thin layer, i.e., a iilrn, and then dried insitu. Drying is accomplished by the evaporation of volatileconstituents, i.e., the temporary organic vehicle or solvent. Shrinkageduring :drying is limited, by coaction between Ythe tape vcarrier andthe iilm, to that which 'takes place perpendicular to the tape carrier;shrinkage of the ceramic-particulate lilm in a -direction parallel tothe tape carrier 'or support'either-does not occur or is so negligiblethat it ldoes not 'impair the quality of the final Atired ceramic, evenif the `ceramic is to be used lin a capacitor. Consequently, shrinkageof the film, if any, occurring in a Idirec-tion par-alici to `the tapesupport may accurately be termed negligible. The flexible dried filmremains 'light-ly adherent on the :tape support.

The film, still intimately in contact with the supporting tape surface,may now be rolled ontoa lreel or ymay be subjected immediately tofurther processing steps such as cutting, molding, stamping, and thelike, as hereinafter explained.

A Wide variety of thin ceramics-may be made using the process of thisinvention. lFer dielectrics, inorganic materials consisting chiefly ofalumina, steatite, Zircon, aluminum silicate, zirconium dioxide,titanium dioxide, magnesium silicates, etc., and various combinationsthereof, Iare preferred, but are only examples of raw materials whichmay be employed. vThe `ra-w `material selected for the Yslip is groundto a tine particle Isize, on the order of minus 325 mesh or smaller forextremely thin ceramics, but larger, eg., -on the order of minus 200mesh, if thicker ceramics are to kbe formed, 'and still larger if it isnot important lto obtain thin nonporous fired materials. Smallerpar-ticle "sizes on the order of minus 325 mesh or the likefacilitate`the formation of a dense, ceramic-particulate film, and aid in gettinga dense fired product, which 'is to be desired when the ceramic is to beused in a capacitor. Larger particles result in a red article ofsubstantially less dielectric strength, frequently of va jporous `orpermeable nature, and-even of la fractured orrstriat-ed complexion. Byusing a ceramic-particulate of a preferred small isize, a finished firedceramic may Vbe made having --a thickness on the order of l mil.

Depending upon the raw material, the density o'f the product will vary,but for use in a capacitor the-density of the fired ceramic shouldyapproach :the theoretically possible iigure for the raw materialselected. -High dielectric strength vthin rcapacitor fdielectrics lmaylhe 'made by this invention which exhibit a porosity, as measured bywater absorption, of less than 0.02%. Of course, the refractorycharacteristic of a raw material affects the quality of the end productand must also be considered in the manufacture of components forcapacitors and the like, as is understood in the art. Reference is heremade to two patents teaching high dielectric constant ceramics, Nos.2,429,588 and 2,626,220 to Hans Thurnauer and lames Deaderick.

Thin, dense and non-porous ceramics may be obtained according to thepresent invention by forming a slip having a high content of finelydivided ceramic-particulate, an organic solvent preferably of lowboiling point, a wetting agent, and a minimum of a binder composition ofthe type herein described. These slips will have varied properties,depending upon the inorganic content, but will usually have a specificgravity of between 2 and 2.6.

The binders of this invention serve to retain the ceramic-particulate inundisrupted position after the organic solvent is evaporated from theslip and, together with the organic solvent and wetting agent,facilitate the formation of dry, flexible films of the particulatematerial free of pinholes, cracks and other imperfections.

A preferred binder composition and wetting agent is as follows:

Percent Polyvinyl butyral 2.5 Polyalkylene glycol derivative 1.0 Alkylether of polyethylene glycol .2

The above percentages are by weight of the nel compounded slip.Accordingly, with toluene by weight present as a solvent, 76.3%ceramic-particulate (e.g. 75% barium titanate and 1.3% calciumphosphate, tribasic) is present in the slip.

Polyvinyl butyral is a thermoplastic organic resin having acomparatively low heat-distortion point of 130 to 140 C. In commerce itmay be obtained under the trade name Butvar from the Shawinigan ResinCorporation. Polyvinyl butyral is an example of a soluble,thermoplastic, volatilizable, vinyl type resin which may be employed.

A suitable polyalkylene glycol derivative to employ in this bindercomposition is triethylene glycol hexoate which has a viscosity ofapproximately 2,000 centipoises and is a compatible plasticizer forpolyvinyl butyral, that is, the triethylene glycol hexoate will notseparate out into a separate phase. In the binder, the triethyleneglycol hexoate functions to improve the exibility and workability of thesolvent-free lrn.

A preferred alkyl ether of polyethylene glycol is the ethyl etherthereof. It functions as a wetting agent, is non-ionic and an excellentpenetrant. A commercial product sold under the trade name Tergitol byCarbide and Carbon Chemicals Company contains lower alkyl ethers ofpolyethylene glycol and may be used as a wetting agent in the abovebinder composition. Compositions without a wetting agent may give ailexible and moldable ceramic-particulate film, but require longermixing periods to obtain the desired uniformity and viscosity in a slip.Use of a wetting agent is preferred as this agent also imparts betterspreading and working characteristics to the slip, as well asfacilitates the formation of an article free of pinholes.

The binder constituents, wetting agent, solvent and ceramic-particulateare thoroughly mixed in apparatus such as a pebble mill to gain asmooth, uniformly dispersed or suspended slip. This procedure may bevaried, if desired, by first compounding the non-vetriiiableformulation, that is, the binder, ingredients and wetting agent, withthe organic volatile solvent, and then adding the ceramic-particulate.The resulting slip has a consistency of thick cream or molasses.

To attain the proper strength and liexibility in a solvent-free filmaccording to this invention, a variety of compatibly plasticizedthermoplastic binder systems may be used. For example, polymethylmethacrylate resin compatibly plasticized with methyl abietate has beenfound to be a successful plasticized resin combination to gain thedesired effects. Ethyl alcohol is a preferred solvent for thiscombination.

Cellulose acetate butyrate resin compatibly plasticized with dimethylphthalate, or tricresyl phosphate, and dissolved in acetone as aSolvent, has also been found to form the desired uniform films of thisinvention.

The above specific examples of suitable binders are not meant to belimitative. Other soluble, thermoplastic, volatizable, organic resinsmay be employed satisfactorily as binder components to give asolvent-free, flexible, moldable and workable ceramic-particulatematerial. The thermoplastic resin selected may be hard or soft, high orlow in viscosity, but must be volatizable during tiring of the moldedarticle to a rigid ceramic. in the case of extremely soft,viscous-liquid polyacrylate esters, that is, those of long chainalcohols, a binder composition may be formed without the need for anadded plasticizer, as long as the viscosity in the resulting slip at ahigh ceramic-particulate content, at least above 70%, and preferablyabove 75% by weight, and a solvent content by weight on the order of20%, remains at the consistency of molasses or thick cream. These resinsof low viscosity may be said to be internally plasticized and,therefore, are considered to fall within the scope of the termcompatibly plasticized resins. In the case of extremely hardthermoplastic resins, such as soluble petroleum derivative resins, ahigher plasticizer content is necessary in the binder composition toobtain a slip of suitable viscosity and workable characteristics andwhich Will give a iilm or cohesive mass having moldable and workableproperties once the organic volatile solvent is volatilized therefrom.As would be expected, the amount of plasticizer required decreases withthe decrease in hardness of the resin. It may be observed here that aresin and plasticizer combination is selected to gain a viscous-liquidmass of resin and plasticizer, that is, a viscous-liquid plasticizedresin mass at room temperature.

Using a plasticizing agent in my binder composition serves to enhancethe lm forming characteristics of the resulting slip as well as lowerthe temperature at which the asolvent, flexible, ceramic-particulatematerial will remain permanently flexible, moldable and workable. Ineach case, the plasticizer selected must have a specificity, acompatibility, for the particular organic resin with which it is to beemployed in a binder composition and must also be soluble in the organicvehicle chosen. For example, alkyl phthalates, abietates and glycolatesare all compatible plasticizers for polyvinyl butyral, and are solublein common volatile organic solvents for the polyvinyl butyral.

The wetting `agent in the binder composition facilitates the formationlof homogeneously uniform slips having desirable spreadability.Additional examples of wetting agents are ethyl phenyl glycol, or otheralkylarylpolyether alcohols, polyoxyethylene acetate, or otherpolyoxyethylene ester, and the like. Without such an agent, excessivemixing is required and uniform films free of imperfections are extremelydiicult to form. With it, the process becomes surprisingly simple. Thewetting agent selected must, of course, be soluble in the organicsolvent used for the plasticized resin, be compatible therewith, andpreferably is of an organic nature so that it is volatilized duringtiring. While ionic inorganic wetting agents may be used, better resultsare obtained with volatilizable organic wetting agents which arecompatible with other components of the slip. By compatible it is meantthat the agent will not separate out from the other components,

The total amount of non-vitriiiable components, that is, plasticizedresin, wetting agent and the like, which may be present in an asolvent,ceramic-particulate film 'having properties as desired may vary fromapproximately 3% to approximately 15%, but preferably is between 3 andfor capacitor dielectrics. The amount of wetting agent employed is onlya relatively small proportion of the total of the non-Vitriiablecomponents, and in most films does not exceed approximately 2 or 3% ofthe dry weight of the film.

Any volatile, low boiling point (e.g., preferably approximately on theorder of the boiling point of toluene or below), organic solvent inwhich all non-vitrifable components of the slipare soluble is suitableto employ. Examples of solvents are toluene, ethanol, butanol, acetone,methyl isobutyl ketone, isopropanol, diacetone alcohol, benzene and thelike, but the specific temporary organic vehicle selected for use as thesolvent must be one in which the resin, plasticizer and wetting agent ofthe slip formulation are allsoluble.

After gaining a slip of a viseocity which may vary from approximately400 to approximately 1200 centipoise seconds, and which may becharacterized as of the consistency of molasses or thick cream, the massis deaired by means well known in the ceramic art. At this point theslip is still maintained at the consistency of molasses or thick cream.Deairng accomplished, the slip is transferred to a slip reservoir whereit is suitably maintained in a uniform homogeneous state -by anagitating arm. The agitation effected by any agitating arm is neverallowed to proceed to the point where air is entrained in the body ofthe slip.

From the reservoir the `slip is discharged through a small orifice in apool onto a substantially-horizontal, flexible, supporting tape. Theflexible supporting tape may be of any impervious, non-porous material,such as polytetrafluoroethylene (Teflon), glycol terephthalic acidpolyester (Mylar), cellulose acetate, cellophane (regenerated cellulose)and the like. A cellulose derivative is preferred. 'Ille advantage ofusing materials of this type lies in the fact that great uninterruptedlengths of a uniform supporting surface may be passed beneath thedischarge orifice. Interruptions o-f the process are, therefore, lessfrequent than with other processes, and irregularities in the flexibleceramic-particulate film are avoided. However, any suitable impervious,non-porous, smooth, insoluble, flexible materials may be employed as thesupporting tape.

The slip, e.g., one formulated with the preferred binder and wettingagent as set forth above, deposited in a pool on the supporting tape, isthen slightly compressed, spread and leveled. While I use a method ofdepositing the slip on the tape which amounts to fundamentally a pouringaction, other methods of placing the slip on the tape may be employed,methods such as extrusion included. After being spread on the supportingtape surface, volatile constituents of the slip--in the preferredembodiment, the tolueneare removed by evaporation. Removal of thevolatile constituents from the film of slip is accomplished at a raisedtemperature and at a rate depending upon the thickness of the film. Thetemperature should not exceed the boiling point of the particularsolvent employed, temperatures slightly below 80 C. being preferredsince at higher temperatures the film of ceramic-particulate materialhas a tendency to bubble up and form cracks and pinholes. The factors oftemperature and rate of drying are controlled by passing heated air in acountercurrent direction to the movement of the coated supporting tapethrough a drying chamber. This operation may be accomplished in as shorta period as two minutes for extremely thin coats and in progressivelylonger periods as the thickness of the film of ceramic-particulatematerial is increased. It is preferred to dry thick coats atsubstantially lower temperatures, on the order of 30 to 50 C., thanthose employed when dealing with thin coats, which can be dried suitablyat temperatures as high as 80 C., inasmuch as with thick coats of slipsthere is a tendency at higher temperatures `toward drying-crustformation before all volatile constituents of the temporary vehicle haveescaped from the center of the slab. If a thick film or coat of ceramicis desired, a highly volatile solvent such vas acetone, depending alsoupon the nonvitrifiable components, may be employed advantageously. Inthe usual case, rdrying is suitably accomplished by merely passing a twoinch wide, tape-supported slip-film at approximately '3 linear feet perminute through an approximately 8 foot long drying chamber.

After volatile constituents have been removed, the tapesupported driedfilm may be wound upon a reel. The,

/dried film is an intimate blend of inorganic materials in a matrixcomprising binder and wetting agent, and remains flexible even after anextended period of storage. in most cases, however, this storage periodis short, the film usually being immediately subjected to furtherprocessing. Using a thin flexible film of ceramic-particulate such asherein disclosed permits the manufacture of highly dense ceramicdielectrics, on the order of l mil in thickness, by rapid, automaticprocesses.

Referring now to the figure inconporated in and made a part of thisspecification, it is seen that a slip reservoir 10 is placed immediatelyabove a supporting conveyor tape 11. A stirrer (not shown) may beemployed within the slip reservoir to agita-te the slip, that is, thesuspension of ceramic-particulate, without entrainin-g air. The slipreservoir terminates in la small nozzle 12 with an orifice in its end ofapproximately 1/16 of an inch in diameter. While I prefer a dischargenozzle with an orifice 0f approximately 1/16 of an inch in diameter,other discharge slot shapes may be employed. A pay-out roll of flexible"supporting tape 13 is mounted with a friction clutch (not shown) toallow the flexible tape to be peeled therefrom vonly under a slighttension, thereby to prevent the tape from unwinding in excess. The tapemoves over a suppont iron 14 where slip is received, and then passesbeneath -a doctor blade or bar 15 where the slip is spread, leveled andslightly compressed against the tape. Guide panels may be used on eachside of the doctor blade to prevent waste of slip by any actionspreading it off the tape. The flexible supporting tape 11, coated toeach edge with slip, then passes between two baffles 16 and 17, onebelow and one above the tape, into a drying chamber 18. The dryingchamber is preferably approximately 8 feet long and is fitted with aplurality of spindles 19 to support Ithe flexible tape as it passestherethrough. These spindles 19 are spaced at different levels so as toform somewhat of an arc the length of the drying chamber. This isrequired when heating extremely thin fil-ms of ceramic-particulate onflexible tapes inasmuch as the tape itself undergoes some warping whensubjected to heat. Heated air is passed in a counter-current directionto that direction taken by the passage of the flexible supporting tapethrough the drying chamber. A-t the end of the drying chamber theEbaffles serve to deflect the air from that tape which has just beencoated with slip and prevent premature drying action at the point ofspreading and leveling of the slip on the tape. The coated tape vpassesbetween rollers 20 and 21 and is drawn through the apparatus by theserollers, roller 20 being supplied with low geared power and roller 21pressing resiliently thereagainst. The coated tape is then wound on areel 22.

The solvent-free, flexible, ceramic-particulate film may now besubjected conveniently to any necessary process before =being fired tovitrification. It has the property of being slightly elastic whensubjected to stress and may be fired under stresses, e.g., fin arcuateform, without untoward-development of areas of poor dielectric strengthdue to strain in the product. ln 'the flexible dried state, the amountof ceramic-particulate in the film formed with the preferred bindercomposition and wetting agent in amounts as set forth above is around96%. In the usual case, the amount of ceramic-particulate in the film tobe used as a dielectric shold lbe above 90%, and, preferably shouldapproach 96 or 97%. As low as 85% may be employed, but this renders thefilm undesirable for use in the manufacture of components forcapacitors. Generally speaking, it is the high ceramic-particulatecontent of my flexible films which makes them so desirable for use inthe manufacture of dielectrics. With such a high content of non-filmforming ceramic-particulate constituents, it is surprising that anasolvent, flexible, tough, slightly elastic film as disclosed herein canbe formed.

A solvent-free film having a high content of barium titanate, or thelike, as disclosed in the above referenced patents, may be used in themanufacture of capacitor plates. Referring to Figure 2, the tapesupported ceramicparticulate, eg., barium titanate, film 23 is drawnfrom a reel 24 beneath stationary cutting surfaces 25 which act to slicethe film longitudinally. Figure 3 is an enlarged cross section of thesecutting surfaces taken along line 3 3 in Figure 2, and shows an enlargedView of the cutting knives 25 penetrating only the ceramic-particulatecoating 26 on the tape 38. The tape supported lm is pulled in a tautmanner beneath these cutting surfaces by rollers 2.7 and 2S, roller 27being powered and roller 28 pressing resiliently thereagainst. The tapesupported lm is then allowed a compensating lag 29 before it is advancedintermittently, by `and between resiliently opposed rollers 30 and 31,beneath a synchronized transverse cutting edge 32, which acts againstsurface 33, with :a tolerance within approximately 0.()02

' of an inch, to cut the film without cutting the supporting tape. Atthis stage the ceramic-particulate film has been cut into a plurality ofsmall square or rectangular units supported on the flexible tape. Thetape supported units then `are wound on a roll 34. From the roll 34, theunits are transferred to refractory plates by an unusually unique stepin this art. A strip of tape holding the cut film, as illustrated `inFigure 4, is pulled off the reel, inverted, that is, placed film sidedown on a refractorysetter plate 35, as illustrated in Figure 5, andstripped from Ithe ceramic-particulate units 36, leaving them inposition for firing. The small square or rectangular units ofceramic-particulate remain loosely adherent to the supporting tape and,therefore, the inversion of the tape need not be accompanied by anyspecial precautions. To accomplish the removal of the tape from thesmall units 36 of ceramic-particulate in a swift manner, a rod 37 isplaced on top of the inverted tape 38 and the tape peeled from the cu-tunits by pulling it around this rod. In order to do this in a manner toprevent adherence of the small cut units to the withdrawn tape andconsequent distortion of the units, particularly arcuate distortion, therod must be of a small diameter, preferably on the order ofapproximately 1/s of an inch. It will be seen that a `great number ofthin capacitors may be made continually by my process in a short periodof ltime and in ya substantially automatic manner. While I showparticularly cutting of the fiexible film, other methods of forming thefilm into articles, methods such as scoring, stamping and the like, maybe employed. Ceiling and arching of the film separated from thesupporting tape, and firing it in a coiled or arched state, is alsopossible without untoward occurrence of areas of poor dielectricstrength due to strains in the fired product.

If desired, cakes lof moldable, cohesive, ceramic-particulate masses maybe formed by a variation of the process above, such a process comprisingextruding a highly viscous slip of ceramic-particulate in a layer onto aconveyor, and drying it as set forth above with respect to the drying ofthick films at lower temperatures and at a slow rate. The solvent-free,cohesive aggregate or mass of inorganic materials may be molded byimpact, injection or other means as desired. It remains workable untilred to a rigid ceramic.

Asolvent, flexible strips of extruded or coated ceramic- 'particulatematerial hereof may also be employed in the manufacture 4of a number oflike parts by an unusual simultaneous stamping and molding process, theparts, thereafter, being fired to vitrification.

The simultaneous stamping and molding of these strips or thick films,preferably after they have been separated from a supporting surface, maybe accomplished to only a partial state, i.e., the stamping operationmay be used to mold in the strip an article which still clings to thebody of the strip. In effect, the molded article is merely scored in thestrip. In this condition, the strip is fired and the molded article orarticles later separated from the strip.

I do not wish to be limited in the scope of my invention defined aboveexcept as set forth in the appended claims.

I claim:

LA process of making ceramics comprising formulating a slip of ahomogeneous character and adapted for use in forming dense ceramics,said slip comprising a high content of ceramic-particulate, a volatileorganic temporary vehicle, and a compatibly plasticized thermoplasticbinder resin which promotes the formation of fiexible films and which issoluble in said vehicle, spreading and coating said slip in a film on asmooth flexible movable supporting tape, removing the volatile temporaryvehicle from the film while simultaneously retaining the remainingcoated constituents of said slip in adherent relation to the flexiblesupporting tape and supported thereby, and firing the vehicle-freeflexible film to a rigid ceramic.

2. A process as in claim l in which the film comprisingceramic-particulate is formed, after removing the volatile temporaryvehicle, into articles while supported by the supporting tape.

3. A process for making thin ceramics comprising formulating a slip of ahomogeneous character and adapted for use in forming dense ceramics,said slip comprising sufficient ceramic-particulate to account for atleast o-f the solids material of said slip, a volatile organic temporaryvehicle, a compatibly plasticized thermoplastic binder resin, and awetting agent compatible with the plasticized resin, said plasticizedresin and wetting agent Ibeing soluble in the temporary organic vehicle,spreading said slip in a film on a smooth flexible movable supportingtape, removing the volatile organic temporary Vehicle from said slipwhile simultaneously retaining the remaining film constituents of saidslip in adherent relation to the flexible supporting tape and supportedthereby, forming the flexible, vehicle-free film of ceramic-particulateinto articles, and firing the formed articles to a rigid ceramic.

4. A process as in claim 3 in which articles formed from thevehicle-free film of ceramic-particulate material are thereafter archedand fired in arcuate form.

5. A process as in claim 3 in which the resin is a polyvinyl typecompatibly plasticized with a polyalkylene glycol derivative.

6. A process as in claim 3 in which the vehicle-free, flexible film ofceramic-particulate, while supported on the tape, is cut by drawing saidtape-supported film in a taut manner and at a uniform rate of movementbeneath longitudinal cutting means, and by advancing said tapesupportedfilm intermittently through synchronized lateral cutting means.

7. A process for making thin ceramics comprising formulating a slip of ahomogeneous character and adapted for use in forming dense ceramics,said slip comprising sufficient ceramic-particulate to account for atleast 85% of the solids material of said slip, a Volatile organictemporary vehicle, and a compatibly plasticized organic binder resin,spreading and leveling said slip in a film on a substantiallyhorizontal, smooth flexible movable supporting tape, removing volatileconstituents 'from said slip at a raised temperature up to approximately9 80 C. to leave it in a solvent-free condition while simultaneouslyretaining the solvent-free, tiexible lm of ceramic-particulate inintimate adherent relation to the supporting tape and supported thereby,cutting the iiexible film While adherently supported on the tape,resting said cut iilm in contact with a refractory surface, removing thecut lm from the flexible supporting tape Without arcuate distortion ofthe film by peeling the tape over itself from the lm, and tiring thesaid iilm to a rigid ceramic.

8. A solvent-free, moldable, cohesive flexible lm in the form of alength of tape, said film Lbeing reable to a rigid ceramic state andcomprising an intimate blend of more than 90% vitriiable inorganicmaterials in particulate form, an organic-solvent-soluble compatiblyplasticized thermoplastic `organic binder resin, and a non-ionic organicwetting agent compatible with said plasticized binder resin.

9. A solvent-free, cohesive Ilayer in the form of a length of tape, saidlayer being fireable to a rigid ceramic state and comprising an intimateblend of more than 85% inorganic materials in particulate form, anorganic-solvent-soluble thermoplastic organic binder resin, a compatibleplasticizer for said resin, and a non-ionic organic wetting agentcompatible with the plasticized resin, said layer being characterized bya flexibility at room temperature.

10. A solvent-free flexible cohesive layer in the form of a eXiblelength of tape, said layer comprising an intimate blend of more than 85%ceramic particulate, an organic-solvent-soluble thermoplastic polyvinylbutyral binder resin, and a compatible organicsolvent-solublepolyalkylene glycol plasticizer for said resin, said layer beingcharacterized by being flexible at room temperature as well as by beingfireable to a rigid ceramic state.

11. As an article of manufacture: a thin strip of flexible solvent-freegreen ceramic supported in adherent relation upon a removable smoothflexible supporting tape, said green ceramic strip being solvent-freeand comprising an intimate blend of at least 85% ceramic particulate, anorganic-solvent-soluble thermoplastic organic binder resin, and anorganic-solvent-Soluble cornpatible plasticizer for said resin,

12. A process of making ceramics comprising formulating a slip of ahomogeneous character and adapted for use in forming dense ceramics,said slip comprising suficient ceramic particulate to account for atleast 85% of the solids material of said slip, a volatile organictemporary vehicle, and a compatibly plasticized organic binder resinwhich promotes the formation of exible ilms and which is soluble in saidvolatile organic temporary vehicle, coating said slip in a ilm upon asmooth liexible moving supporting tape, evaporating the volatiletemporary vehicle from the coated film While simultaneously retainingthe remaining coated constituents of said slip in adherent relation tothe flexible supporting tape and supported thereby, then stampingarticles out of said resulting vehicle-free exible iilrn, yand ring thearticles to a rigid ceramic.

13. A process as in claim 12 in which the vehicle-free exible film isstripped from the supporting tape prior to stamping the articlestherefrom.

14. A process for making a exble, vehicle-free cohesive layer comprisingat least inorganic materials which may be red to a rigid state, saidprocess compris ing formulating a slip of a homogeneous character andadapted for use in forming dense ceramics, said slip comprisingsufficient vitriable inorganic materials in particle form to account forat least 85% of the solids material or" said slip, a volatile organictemporary vehicle, and a compatibly plasticized organic binder resinwhich promotes lthe formation of flexible layers and which is soluble insaid organic vehicle, coating said slip on a smooth flexible movingsupporting tape, evaporating the organic temporary vehicle from saidlayer of coated slip While simultaneously retaining the remaining coatedconstituents of said layer in adherent relation to the flexiblesupporting tape and supported thereby, and then forming saidvehicle-free iiexible cohesive layer into articles prior to firing thesame.

15. A process as in claim 14 in which the vehicle-free exible cohesivelayer is Wound into a storage roll before forming articles therefrom.

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